This is the Generation 2 Planet Waves NS (Ned Steinberger designed) Micro Headstock Tuner in a two pack!. The NS Micro Headstock Tuner offers improved accuracy, faster response, expanded calibration range, and an improved ratchet design*.
A highly sensitive piezo transducer and easy to read multi-color backlit display allow smooth and highly accurate tuning in noisy, dim or well-lit environments while the micro design and reversible screen allow the tuner to hide effortlessly behind or mount on the front side of the headstock allowing the tuner to remain clamped to the instrument inside most cases when stored. A 360 degree swivel mechanism and adjustable padded clamp, offers optimal viewing angles and maximum positioning flexibility. As a result, the NS Micro is equally at home on left and right-handed instruments as well as on small and large headstocks, making it the ideal choice for the widest variety of players and instruments. The NS Micro is powered by a readily available CR2032 battery (included) and provides maximum battery life utilizing an auto-off function, shutting the tuner off automatically after several minutes from power up.
Enjoy effortless and inconspicuous tuning at a great value with the NS Micro Headstock Tuner. A Ned Steinberger design.

Built-in piezo transducer picks up instrument’s vibration rather than sound Improved software for faster response and improved accuracy Tri-color reversible backlit LCD screen makes it easy to tune in dark environments while allowing mounting in front or behind headstock Wide calibration range (410Hz to 480Hz)
Compact design blends into the aesthetics of instrument while adding considerably less weight than other headstock tuners Tunes acoustic and electric guitars, basses, mandolins, banjos and other stringed instruments  
* Compared with previous Planet Waves Mini headstock tuners